The invention concerns a drive system for a motor vehicle with a combination starter-generator unit.
In accord with conventional usage, internal combustion motors of powered vehicles have been driven at such speeds of rotation by means of a starter, which is a direct current motor, that the internal combustion motor can then function of its own accord. As this happens, the starter motor torque is transferred by means of a pinion gear to the flywheel of the motor. This known starter is so flanged to a motor block so that, upon a start procedure, the pinion gear meshes with a ring gear on the flywheel in order, thereby, to set the motor into rotary motion.
An internal combustion motor is normally brought to a rotary speed of ca. 300 RPM by the starter. From this relative small speed of rotation, an internal combustion engine will become self energizing and regulates itself to an idling rotational speed which, for example, runs about 700 RPM. When the internal combustion motor is running, then a separate generator current is produced for charging the vehicle battery. The said generator is usually run by a V-belt or toothed belt drive connection.
In separated systems of this type, two electrical machines are disadvantageously installed, the first for the starting an internal combustion machine and the second for the production of the said current, whereby the advantage of an electrical machine, which is that it can be run both as a generator as well as a motor, is not made use of.
In order to efficiently design the current supply of a motor vehicle, increasing developments have been undertaken which have the goal of combining the function of starting motor and current generation into one component.
One of the solutions to the problem has been made known in the publication xe2x80x9cEuropean Automotive Designxe2x80x9d, issue for April 1998, pg. 24. In this case, an electric motor is connected directly with the crankshaft of the internal combustion motor. By means of the electric motor, which is installed as a power device between the internal combustion motor and the transmission, the starter function and the generator function can be both carried out. In this case, the design of the electric motor is essentially directed toward the starting requirement.
Together with power electronics and a start-condenser as a storage medium, this known electric motor now replaces a conventional starter, the generator and the flywheel of the motor vehicle and controls, as a generator, the supply of electrical energy.
Looking toward the future and giving consideration to the installation of start-stop automation, by means of which the internal combustion motor will be shut off during vehicle stillstand to save fuel, progressively shorter startup times with simultaneous noise level reduction will be demanded. This involves an increase in the loading on the starter and an increase in size of the electric motor which will then be over-dimensioned for operation as a generator. Further, the installation of larger electric motors, because of the very limited available space, leads to additional problems.
In order to be able to install a smaller motor as a starter, it is possible to install an intermediate drive, i.e., a starter-drive, between the electric motor and the crankshaft in order to make the necessary torque to the crankshaft during the start available.
After the start has been consummated, however, the ratio in the generator train is undesirable since the generator should be driven in concert with the crankshaft rotation in order to develop a corresponding charging current. In order to make this possible, a starter-drive, which possesses a planetary drive with clutch procedures or overrunning clutches, is tried. In this arrangement, during the starting operation a ratio of i=3 to i=4 is employed while, in the generator mode, a ratio of i=1 is made possible.
The starter-drive for the above described application is placed in an intermediate housing as a self-sufficient component between the internal combustion motor and a torque converter of the vehicle transmission. The said starter drive disadvantageously exhibits an installation size which, to a certain extent, favors the advantages of smaller motors.
Another problem is the time and cost disadvantage of construction with a substantial multiplicity of components, wherein air removal of a rotating unit and a self contained lubrication system is necessary. Additional dynamic sealing means were required, for the sealing of the intermediate housings, which disadvantageously give rise to an increased torque drag.
The purpose of the present invention is to create a drive system for a motor vehicle wherein the advantages of an electrical machine are used to the extent that purpose further encompasses an integration of the said electrical machine into the drive train in the most simple constructive manner and to accomplish the said integration in small space requirement.
In accord with the invention, this purpose is achieved by a drive system.
In the case of the drive system in accord with the invention, in every case, the expense in time and money and the number of the components is reduced, whereby, in an advantageous manner, the motor compartment space and weight are minimized and the costs of manufacturing are lowered.
Besides a simplified lubrication sealing and ventilating method by means of the integration of the starter and generator unit into an assembly of the drive train, the efficiency is increased because of discarding additional dynamic sealing means in comparison to a construction as a self-contained component.